In recent years, a wide range of articles including documents, artistic works, various commercial products and banknotes have been targets for intense counterfeiting efforts. In a widespread attempt to deter the production of illicit copies, various techniques have been developed for identifying or authenticating genuine articles. For example, U.S. Pat. No. 4,423,415 entitled "Non-Counterfeitable Document System" (Dec. 27, 1983) discloses systems and techniques for effectively authenticating specific genuine articles.
Although prior art systems and techniques have considerably deterred counterfeit operations, problems continue to exist, particularly with regard to certain articles. For example, paper currency continues to be the objective of considerable counterfeiting activity. Aspects of currency production and the manner in which money circulates tend to raise special problems. For example, banknotes are subjected to considerable abuse resulting from extensive handling. In routine commerce, banknotes are folded, crumpled, soiled and abraded.
A number of techniques have been proposed to authenticate banknotes by recognizing the generic characteristics of specific monetary issues. For example, characteristics of paper, printed material and paper additives have been tested to distinguish valid and invalid currency. Although such systems have met with substantial success, problems continue to exist. For example, if a test criteria is generic, i.e. applicable to all banknotes of a specific issue, counterfeiters are afforded a substantial degree of tolerance in their efforts to duplicate. That is, authentication techniques which use the same criteria to verify thousands of banknotes must be far less discriminating than a technique applying specific criteria to identify a specific banknote. However, known techniques for individual authentication of banknotes raise other practical problems.
As mentioned above, banknotes change as a result of wear, wrinkling and soiling. Consequently, the typical substantial alteration of banknotes imposes a special problem for individual authentication. As another problem, the available space on a bill for subtle code marks may be somewhat limited. Additionally, production economy is usually important and authentication should involve simple and economical apparatus. Accordingly, a need exists for an improved system to test and authenticate currency.
Various other articles also have presented special problems for reliable authentication. For example, some effective prior authentication systems involve the passage of light through an article being tested. Of course, such a technique cannot be used on opaque articles. Additionally, some of these objects may be relatively small. Accordingly, the need exists for an improved economical and effective authentication system for various opaque and small objects such as machine parts, integrated circuit chips and pasted-on labels.
In general, the system of the present invention is directed toward the authentication of various articles including currency, opaque objects and small items. The system characterizes articles with an efficient and effective code that accommodates various problem articles. Specifically, the system allows for considerable deterioration in currency and may also be used in cooperation with sensing techniques for opaque and small articles. Furthermore, the developed characterizing identification may be recorded in a format that requires relatively limited space. Additionally, the format facilitates easy comparison and simple sensing, e.g. it may be embodied in a self clocking configuration.
In accordance with the system of the present invention, the observed characteristic of an article is dissected into data elements or pixels which are quantized into one of three possible values. For example, in a currency system, the translucency of a banknote may be sensed at several discrete areas after which the resulting signals are quantized to manifest each area as: (1) definitely darker than the average reading, (2) definitely lighter than the average reading or (3) close to the average reading. As will be apparent from the detailed descriptions below, such characterization accommodates effective verification in spite of currency deterioration and is effective for characterizing certain phenomena as may be taken from opaque objects.
With regard to opaque objects, in accordance herewith, interfering light is utilized to develop characterizing patterns. For example, two beams of light are reflected from a specific area location on the object under investigation. The wavefronts of the beams are directed so as to interfere with each other and as a consequence an interference pattern is generated in the manner of an interferogram. Such patterns manifest peculiarities of a specular surface, e.g. one which is somewhat irregular. Such patterns tend to be binary, that is, interference either is present or it is not present, thus producing either darkness or light. In accordance with the present invention, such patterns can be effectively sensed and compared to identify or authenticate an article.
As disclosed in detail below, the system hereof may be variously implemented for operation with various forms of articles, various identification characteristics and various techniques. For example, interferometer techniques may be utilized on products which have no particularly specular surface as by applying an irregular surface. Also, various representation formats may be employed and, of course, a wide variety of techniques may be employed for providing reference identification data.